Spinneret pack



y 1966 E. A. MARTIN 3,259,938

SPINNEREI PACK Filed March 13, 1964 INVENTOR E. A MA RTI N BY W m. 7222/ ATTORNEY United States Patent C) 3,259,938 SPINNERET PACK Eugie A. Martin, Pensacola, Fla., assignor to Monsanto Chemical Company, St. Louis, M0., a corporation of Delaware Filed Mar. 13, 1964, Ser. No. 351,721 Claims. (Cl. 18-8) This invention relates to the melt spinning of synthetic yarn. More particularly, the invention pertains to a new and useful apparatus for melt spinning synthetic yarn.

Frequently, in melt spinning employing contemporary spinneret packs, individual filaments vary in denier and composition along their respective axes. These variances result in excessive breaks, wraps, and generally poor quality yarn. Variable resistance to flow within a pack is a primary cause of many yarn quality deviations. Because of variable flow resistance, polymer flow rates within a spinneret pack vary in magnitude; therefore, many spinneret capillaries receive greater polymer flow than do other capillaries in the same spinneret, resulting in variable denier filaments.

A second problem in the usual spinneret pack is excessive formation of gel. Gel formation is related to polymer residence time within a pack, the longer the residence time of a particular fluid particle, the greater the tendency for gel formation. Many times gel will form in a sand pack, then find its way into a spinneret capillary, thereby restricting or terminating polymer flow through the affected capillary. Stagnant areas within a spinneret pack appear to be primarily responsible for variable fluid particle residence time therein. Fluid particles in a stagnant area have a much greater residence time than do fluid particles in normal flow lines. Stagnation of such fluid particles allows the polymerization process to reach an undesirable stage, gel formation, with all of its attendant problems.

An object of the invention is to produce a spinneret pack having a nearly constant flow rate across its entire pack cavity cross-section.

Another object it to produce a spinneret pack having reduced stagnation areas.

A further object is to provide a spinneret pack wherein the flow resistance from polymer inlet port to capillary for any fluid flow path is approximately equal to that of every other flow path.

Other objects will become apparent from the following description.

Objectives as described above are achieved in the provision of the hereinafter described apparatus. A spinneret pack having a variable cross-section, increasing in the direction of polymer flow and filled with inert granulated porous material, is provided. A fine mesh wire screen is placed across the bottom of the cavity. A distribution plate is attached in sealed relationship to the bottom of the cavity. This plate has a plurality of variable length and diameter capillaries therethrough. These capillaries have their entrances substantially equidistant from that point where polymer enters the pack cavity and are related one to the other by the parameter L/r where L is capillary length and r is capillary radius. A spinneret plate is disposed below the distribution plate in sealed relation therewith.

A variation of the invention is the use of only a spinneret plate without a distribution plate, this spinneret plate also meeting the criteria of having capillary entrances equidistant from the point where polymer enters the pack cavity. The capillaries of this plate are comprised of two cylindrical, axially oriented, communicating bores, the upper bore havign radius 1- and length L both of which vary with respect to other capillaries in the same plate according to the parameter L /r The di- 3,259,938 Patented July 12, 1966 mensions of the lower bore, having radius 2' and length L remain constant with respect to every other capillary in the same plate, all lower bores having smaller dimensions than do their respective communicating upper bores.

In the drawing:

FIGURE 1 is a sectional elevation illustrating the use of the pack cavity base plate as a distribution plate.

FIGURE 2 is a sectional elevation illustrating an embodiment of the invention wherein the pack cavity base plate is a spinneret plate.

Referring now to FIGURE 1, it can be seen that pack holder 10 is the foundation element. Through pack holder 10 polymer conduit 12 is connected to a source of molten polymer under high pressure. Spinneret pack 14 is fitted into pack holder 10 so that spinneret pack cavity 16 is in communicating relationship with conduit 12 and this connection is sealed with annular gasket 18.

Spinneret pack cavity 16 is tightly packed with inert,

granulated, porous material, usually sand; however, other materials such as metal, ceramics, glass and the like are acceptable. Grain size must be small in comparison with the total size of the spinneret cavity. Furthermore, the granulated material should extend for a short distance, e.g., one inch, up into the polymer entrance port. Laid across the base in contoured relationship therewith is screen 29, usually fine mesh wire. Distributor plate 22 is fitted to the base of pack cavity 16 and sealed with annular gasket 24. As can be seen, distributor plate 22 has an arcuate upper surface portion 26 that has the configuration and contour of the arcuate surface of a sphere. Capillaries 30 are shown as having diameters that vary with respect to the diameters of the other capillaries, the diameter of each bore increasing as the length increases. Spinneret plate 32 having constant dimension capillaries 34 is aflixed below distributor plate and sealed with gasket 32. The entire pack apparatus is held in place by annular clamp 38, secured with bolts 40.

The apparatus illustrated by FIGURE 2 is almost identical with FIGURE 1 except that the distribution plate of FIGURE 1 is now, as modified, the spinneret plate of FIGURE 2. In the spinneret plate 42 capillaries 44 do not have constant diameters, but consist of two bores, the topmost varying according to the parameter L/r while the bottom remains constant in length and diameter with respect to every other capillary. Washer 46 is inserted to modify the apparatus of FIGURE 1 to utilize the spinneret plate of FIGURE 2.

Although, generally, the invention has been described primarily from the viewpoint of having only one polymer entrance port, this is not meant to infer that the invention cannot be modified to permit entry of two or more metered streams into one pack cavity. A specific pack cavity embodiment is one having a plurality of metered streams thereinto that would, in effect, be two or more, as described hereinbefore, approximately cone shaped cavities placed side by side with the common wall or walls removed. The base plate would have as many arcuate surface configurations as there are polymer entrance ports, thereby having the important feature that all capillary entrances be substantially equidistant from a poly-. mer entrance port.

As is readily apparent from the illustrative figures, there are few areas, if any, in the pack cavity where flow may be held up, resulting in polymer stagnation and gel formation. Molten polymer flows through the pack cavity at substantially equivalent rates across the entire pack cavity cross-section. It follows from reduced gel formation that the quality of yarn produced will be enhanced. There will be less gel to vary filament composition, thereby reducing wraps, breaks, and the like.

Pressure measurements taken at variable distances from a point flow source indicate that pressure varies inversely with the distance from the point source of flow. These variable pressures may be represented by a series of concentric spheres, the center of which is the point flow source. Each sphere represents a particular flow potential, or pressure.

Flow lines are normal to pressure lines, i.e., flow is from a point of high pressure to areas of lower pressure. It follows that, in the design of a spinneret pack, when a pack cavity shape is chosen that will take advantage of this spherical pressure configuration, an equal pressure at every capillary is possible. A segment of a sphere in the shape of a cone, with its apex at the sphere center and having the base conforming to the arcuate surface of the sphere, would be a good example of a shape that would meet the design criteria of the invention. In the arcuate base plate capillaries therein would each have its entrance equidistant from the point source of flow, i.e., when such source is at the apex of the pack cavity. As a general rule, subject to difficulties in fabrication, any point within the pack cavity should lie on a straight line connecting some point on the bottom surface, including capillary entrances, with the center of the entry port at the top of the cavity, which line does not intersect any boundary of the cavity. Further design limitations are that capillaries be not more than /2 inch apart, counterbored slightly if desired.

Base plates, whether distribution or spinneret, would only have a concavity therein and would not be totally arcuate. On the bottom, the plate would be flat. This would result in capillaries having different lengths, producing variable pressure drops therethrough. It is desirable not only to have equal pressures at the entrances to all capillaries, but also at their exits. To achieve this result, capillaries are designed to conform to the parameter L/r where L is capillary length and r is radius. The parameter, L/r is derived from the Hagen-Poiseuille equation (ref. Unit Operations of Chemical Engineering, W. L. McCabe, McGraw-Hill Book Co., Inc., 1956, pages 50-51) for isothermal, laminar flow of non-compressible fluids in cylindrical tubes:

where P is pressure in pounds force per foot L is tube length in feet; 7 is average fluid velocity in feet per second; ,a is fluid viscosity in pounds per foot-sec; g is Newtons law conversion factor, 32.174 ft.-pounds per pound force-second and D is tube diameter in feet. To change the quantities involved in the equation somewhat where q is fluid flow rate in pounds per foot and r is radius in feet, and

resulting in the equation and M V (4)(32.l7)1r is equal to a constant, C; therefore,

AMA,

From the above relationship it can be seen that as the length of a capillary increases, it must also increase in radius to achieve an equivalent pressure drop in all capillaries.

As has been noted before, there are two methods wherein the arcuate base plate may be used. When used as a distribution plate, polymer emerges from each capillary at essentially the same pressure as at all other capillaries. The polymer then flows through the spinneret capillaries and is quenched to form filaments.

When the arcuate base plate is utilized as a spinneret plate it is much preferred that the exits of all capillaries have the same diameter. Therefore,.the capillaries consist of two aligned communicating bores, the topmost varying according to the parameter L/1 the lower bore remaining constant in both diameter and length with respect to the bottom bore of every other capillary in the plate.

Advantages of the herein described apparatus are numerous. When pressure at all capillary entrances and exits is the same, thread lines having more consistent denier are produced. Reduced gel formation produces filaments having more consistent composition along each filament, i.e., particles of gel are not continually breaking off and clogging or passing through spinneret capillaries. Furthermore, when gel is reduced much less maintenance is necessary for spinneret packs, resulting in substantial savings in both time and money.

I claim:

1. A spinneret pack for melt spinning apparatus comprising, in fixed juxtaposed relation in the direction of polymer flow, the combination of:

(a) polymer conduit means;

(b) means defining a cavity having a variable transverse cross-section increasing in the direction of polymer flow and substantially larger than the polymer entrance port, said conduit means communicating with said cavity;

(c) granulated inert porous material within said cavity;

(d) screening means across the bottom of said cavity;

(e) a distribution plate attached in sealed relationship with the bottom of said cavity;

(f) means defining a plurality of spaced capillaries in said distribution plate, any point on the surface of which is substantially equidistant from the centerline of the polymer entrance port, said capillaries having variable lengths and cross-sectional areas with respect to the other capillaries, said'cross-sectional areas increasing proportionally with increases in capillary length; and

(g) a spinneret plate attached in sealed relationship next below said distribution plate. 2. The spinneret pack of claim 1 wherein the granulated, inert, porous material is sand.

3. The spinneret pack of claim 1 wherein the screen-' 1 ing means is fine wire mesh.

4. The spinneret pack of claim 1 wherein the cavity is cone shaped having a polymer entrance port at the.

apex thereof.

5. A spinneret pack for melt spinning apparatus comprising, in fixed juxtaposed relationin the direction of polymer flow, the combination of: (a) polymer conduit means;

(b) means defining a cavity having a variable .transverse cross-section increasing in the direction of polymer flow and substantially larger than the polymer entrance port, said conduit means communicating with said cavity substantially at the top there 6. The spinneret pack of claim 5 wherein the granulated, inert, porous material is sand.

7. The spinnert pack of claim 5 wherein the screening means is fine wire mesh.

8. The spinneret pack of claim 5 wherein the cavity is cone-shaped having ,a polymer entrance port at the apex thereof.

9. A spinnert pack for melt spinning apparatus comprising, in fixed juxtaposed relation in the direction of a polymer flow, the combination of:

(a) polymer conduit means;

(b) means defining a cavity having a variable transverse cross-section increasing in the direction of polymer flow and substantially larger than the polymer entrance port, said conduit means communicating with said cavity;

(c) granulated inert porous material within said cavity;

(d) screening means across the bottom of said Eavity;

(e) a distribution plate attached in sealed relationship with the bottom of said cavity;

(f) means for defining a plurality of spaced capillaries in said distribution plate, any point on the surface of which is substantially equidistant from the center line of the polyme entrance port, said capillaries being cylindrical and being of variable length (L) and radius (r), the length and radius of the capillaries being related by the parameter L/r and (g) a spinneret plate attached in sealed relationship next below said distribution plate.

10. A spinneret pack for melt spinning apparatus comprising in fixed juxtaposed relation in the direction of polymer flow, the combination of:

(a) polymer conduit means;

(b) means defining a cavity having a variable transverse cross-section increasing in the direction of polymer flow and substantially larger than the polymer entrance port, said conduit means communicating with said cavity substantially at the top thereof;

(c) granulated inert porous material within said cavity;

((1) screening means across the base of said cavity;

(e) a spinneret plate attached in sealed relationship with the bottom of said cavity; and

' (f) means defining a plurality of spaced capillaries in said spinnert plate, any point on the surface of which is equidistant from a fixed point in a particular polymer entrance pout, said capillaries being cylindrical and being of variable length (L) and radius (r), the length and radius of the capillaries being related by the parameter L/r References Cited by the Examiner UNITED STATES PATENTS 2,408,713 10/1946 Webb l88 2,821,744 2/1958 Spohn et a1 18---8 2,932,062 4/1960 Speakman et a1. 18-8 2,971,219 2/1961 Hill 188 3,095,607 7/1963 Cobb 188 3,104,419 9/1963 La Forge 18-8 FOREIGN PATENTS 816,016 7/1959 Great Britain.

58,010 8/ 1946 Netherland. 353,843 6/1961 Switzerland.

WILLIAM J. STEPHENSON, Primary Examiner. 

1. A SPINNERET PACK FOR MELT SPINNING APPARATUS COMPRISING, IN FIXED JUXAPOSED RELATION IN THE DIRECTION OF POLYMER FLOW, THE COMBINATION OF: (A) POLYMER CONDUIT MEANS; (B) MEANS DEFINING A CAVITY HAVING A VARIABLE TRANSVERSE CROSS-SECTION INCREASING IN THE DIRECTION OF POLYMER FLOW AND SUBSTANTIALLY LARGER THAN THE POLYMER ENTRANCE PORT, SAID CONDUIT MEANS COMMUNICATING WITH SAID CAVITY; (C) GRANULATED INERT POROUS MATERIAL WITHIN SAID CAVITY; (D) SCREENING MEANS ACROSS THE BOTTOM OF SAID CAVITY; (E) A DISTRIBUTION PLATE ATTACHED IN SEALED RELATIONSHIP WITH THE BOTTOM OF SAID CAVITY; (F) MEANS DEFINING A PLURALITY OF SPACED CAPILLARIES IN 